A man with masks on a street in Causeway Bay to avoid air pollution. Photo: Dickson Lee

Environment officials came under pressure to cut vehicle emissions after dangerous pollution levels were recorded in one of Hong Kong's busiest shopping districts yesterday.

In Causeway Bay, the air pollution index (API) hit 198, the third-highest level since recording began 18 years ago. Central's highest reading was 187.

Those levels are described as "very high" under the city's pollution forecast and warning system. People with respiratory or heart disease were advised to stay indoors.

In Causeway Bay, the air pollution index (API) hit 198, the third-highest level since recording began 18 years ago

The dominant pollutant in yesterday's air was nitrogen dioxide, which comes from vehicle exhausts or reactions among various pollutants.

Nitrogen dioxide reached 291 micrograms per cubic metre of air at 3pm in Causeway Bay - nearly 50 per cent more than the World Health Organisation safety guideline of 200.

The level of PM2.5 - tiny particles that can penetrate deep into the lungs - was 72.4 micrograms at 3pm. The WHO's recommended safety level is 25 micrograms, on average, over 24 hours. The city's worst recorded roadside pollution was a "severe" API reading of 212 in Central last August.

Dave Ho Tak-yin, principal environmental protection officer, blamed calm weather for the dangerous pollution. "We expect air dispersion will remain poor and the API readings will remain at very high levels in the next couple of days," he said.

Kwong Sum-yin, chief executive officer of the Clean Air Network, called the pollution alarming and urged the government to take prompt action.

"I hope [new measures] can be rolled out at a much quicker pace, and that steps will be taken rather than just talked about," she said.

Officials' top priority, she said, should be retrofitting franchised buses and ageing LPG vehicles with pollution filters.

But a spokesman for the Environmental Protection Department said the government had no timetable for seeking funding from lawmakers to subsidise bus and taxi operators for such a retrofit.

This article appeared in the South China Morning Post print edition as Air pollution soars above WHO safety guidelines